1. Field of the Invention
The present invention relates to roof structures for automobile bodies.
2. Description of Prior Art
Conventionally, an automobile roof structure includes a pair of side rails of a closed cross-section extending longitudinally along the opposite sides of the roof and a roof panel extending between and welded to the side rails. The roof panel has opposite side portions which are laid over the respective side rails to be welded thereto. This type of roof structure has been found disadvantageous in respect of weight since substantial widths of the roof panel side portions are laid over the side rails. In order to overcome the above disadvantage, the U.S. Pat. No. 3,711,147 to S. Higuchi et al discloses an automobile roof structure which uses side rails as auxiliary roof panels. More specifically, each auxiliary roof panel comprises an outer panel and an inner panel respectively having transverse inner and outer flanges. The inner flanges of the outer and inner panels are welded together, and the outer flanges of the outer and inner panels are welded together to form a structure of a closed cross-section. The main roof panel has opposite side edge portions, each of which is welded to the inner flanges of each auxiliary roof panel. A groove is formed between the main roof panel and the auxiliary roof panel at the junction therebetween and a trim strip is placed in the groove.
It has been found, however, that in this proposed roof structure there is a problem of welding reliability between the main and auxiliary roof panels. In fact, when the inner flanges of the auxiliary roof panel are welded together, there are produced irregularities on the flange surfaces due to welded traces so that the side portion of the main roof panel is prevented from coming into intimate contact with the inner flange on the auxiliary roof panel. This will cause a loss in weld strength and warps in the panels.
In order to eliminate the above problems, the inner flanges of the auxiliary roof panel may be extended laterally inwardly so that the welding portions between the inner flanges of are not overlapped with the welded portions between the main roof panel and the auxiliary roof panel. However, this solution is not recommendable because such extension of the flanges of the auxiliary roof panel causes an increase in weight.